1. Technical Field
The present invention is directed to control systems for burner devices for fluid (liquid and gaseous) fuels, and in particular, to burners used for HVAC systems, such as gas-fired burners for furnaces, boilers, heat pumps and the like.
2. The Prior Art
A variety of control systems have been developed for regulating the operation of burners which utilize fluid fuels. Control systems for HVAC systems, in particular, have been the subject of considerable development.
One approach has been to develop a control system which has, as its goal, absolute maximum combustion efficiency. Such a system is disclosed in Foley, U.S. Pat. No. 4,676,734. The Foley '734 apparatus, which can also be used in ovens or stoves, as well as furnaces and boilers, involves the constant alteration of the amount of input air introduced into the combustion process. The combustion output is then monitored, and used as feedback, for the next alteration of input air. Foley '734 further teaches a furnace configuration in which input air and input fuel appear to be varied, in a limited sense, and which has a fixed temperature output of conditioned air.
Another prior art burner control system is disclosed in Krieger, U.S. Pat. No. 4,583,936. The control in Krieger appears to be accomplished through variation of the duty cycle of the burner. Although the flow rate of fuel into each burner is fixed, the amount of time the burner is "on" is varied, in order to vary the thermal input. Air flow into the burner appears variable.
A characteristic which is common to such control systems is that of the various controllable "independent variables," such as gas input rate, combustion air input rate, circulation air rate (for forced air HVAC systems), at most one of these variables is provided with a control capable of operation in other than fixed modes or settings, or are capable of minute variations, in response to changes in operating conditions, such as changes in building load, room damper or vent configuration, etc.
It is desirable to provide a general control system for gas-fired burner apparatus, such as may be used in gas-fired furnaces, boilers, and the like, the separate components of which are capable of operation in more that just a few fixed settings and so are capable of more responsive operation relative to such changes in building load or other operating conditions and requirements.